Previously, we had scenarii to open MySQL server to world: share test databases for workshops, external access for other servers.
Currently, I don't think we still have one of this scenario.
This is the first time someone tries a 3306 port brute force attack but here you are:
Sep 11 19:45:44 ysul mysqld[62132]: warning: /etc/hosts.allow, line 111: can't verify hostname: getaddrinfo(khydc.implodeuniverse.com, AF_INET) failed Sep 11 19:45:44 ysul mysqld[62132]: warning: /etc/hosts.allow, line 111: can't verify hostname: getaddrinfo(khydc.implodeuniverse.com, AF_INET) failed Sep 12 00:25:31 ysul mysqld[62132]: warning: /etc/hosts.allow, line 111: can't verify hostname: getaddrinfo(102.12.52.116.broad.km.yn.dynamic.163data.com.cn, AF_INET) failed Sep 12 00:25:35 ysul mysqld[62132]: warning: /etc/hosts.allow, line 111: can't verify hostname: getaddrinfo(102.12.52.116.broad.km.yn.dynamic.163data.com.cn, AF_INET) failed
I suggest we listen to 127.0.0.1 instead.